APPKNDIX 295 method for determining the number of mctlioxyl groups (OCH-.j present in a compound iZcisel, see p. 220). PREPARATION 78. Hexahydrophenol—llic method of Sabatier and Sen- derens for the reduction of organic compounds is very generally applicable. It consists in passing the vapour of the organic compound mixed with - hydrogen over finely divided metals, especially nickel, as in the example given. Aldehydes and Uotoni's arc. reduced to alcohols*, olefincs to paraffins, and, in the aromatic series, hydrogen is taken up in the nucleus and hydrocyclic compounds result. The hydrocarbons form cyclo- paraflms ; the phenols, cyclic alcohols ; the bases, cyclic amines, &c. PREPARATION 79. o- and p-Nitrophenol. The action of nitric acid on phenol is much more energetic than it is in the case of hen/em.'. To obtain the. mono-derivatives, the acid has, in consequence, to be diluted. The entrance of the nilro-group renders the phenol more strongly acid, so that the nitrophenols, unlike the phenols, form stable salts with alkaline; carbonates. It should be noted that the nitro-groiip enters the ortho- and para-position, but not the meta-position to the Oil group, according to the general rule explained on p. 274. Moreover, the ortho-compound is more volatile than the para-compound. Compare o- and />-hydr- oxybcn/.aldehyde (Prep. Sj, p. i 88). PREPARATION 80. Picric Acid.......The presence of three nilro-groiips converts the phenol into a strong acid. Picryl chloride, which is formed by the action of PC1-, on the acid, behaves like an acid chloride, is decomposed by water and alkalis and forms picramide or trinilraniline with ammonia, <',jll.,(N0,);!n I N1IS r- c:(i!I,(NO,):,Nn,, -1- IIC1. Note that the throe nitro-groups occupy meta-positions in regard to one another ; ortho- or para-positions in reference to t4ic hvdroxvl group.